Any solar heating system, active or passive, can become a cooling system.
Shading the collector during the daytime and exposing it to cool
night time temperatures allows it to lose energy. As the outdoor
temperature rises during the day, the cooler storage medium will
absorb the heat in the home. At night the cycle is repeated, and
the stored heat is given up to the cool night air.
Designing a passive system for cooling requires some form of daytime shading.
A retractable awning or an overhang extension of the roof to shade
the glazing from the high summer sun but expose the glazing to
the low winter sun will suffice. Moveable insulated panels work
better but add to the expense and mechanical complexity. Doors
or glazing panels that open will allow the cool night air in to
remove stored heat.
Active systems can benefit from shading but work almost as well without it. Operating
the collection system at night reverses the energy transfer. Heat
is removed from the storage facility and radiated out the collector.
The storage facility can collect the heat of the home during the
daytime and expel it at night. Areas that do not experience dramatic
temperature swings from day to night or that have warm nights
need a heat pump solar system to capitalize on the reverse flow.
Areas that experience extreme temperature swings, such as the
desert, can construct heat pump systems efficient enough to produce
refrigeration.
Solar cells that produce electricity put a new perspective on cooling. The
electricity generated can power conventional air conditioning
equipment day or night. If sufficient power is not available from
the storage batteries, current from the local utilities can run
the system.
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